For the simulation of solar thermal systems mainly hourly based weather data are used today. The question arises whether short term fluctuations of e.g. solar irradiation that may be present in measured weather data with smaller time resolution has an impact on the result of solar thermal system simulations. To study the influence of weather data time resolutions, different systems that combine solar collectors and heat pumps were simulated with different weathr data time resolution in TRNSYS17.